1. Field of the Invention
The present invention relates generally to a Broadband Wireless Access (BWA) communication system, and in particular, to a system and method for dynamically allocating a connection identification (CID) having a variable length.
2. Description of the Related Art
Many attempts have been made to provide services having a variety of quality-of-services (QoSs) at a rate of around 100 Mbps in 4th generation (4G) communication systems, i.e., next generation communication systems. In particular, the attempts focus on a high-speed data service with guaranteed mobility and QoS in Broadband Wireless Access (BWA) communication systems, such as Local Area Network (LAN) systems and Metropolitan Area Network (MAN) systems, of the 4G communication systems. An Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system adopts Orthogonal Frequency Division Multiplexing (OFDM) technology and Orthogonal Frequency Division Multiple Access (OFDMA) technology to support broadband transmission network to a physical channel of a wireless MAN system. By applying the OFDM/OFDMA technologies to the wireless MAN system, the IEEE 802.16 communication system enables high-speed data transmission by transmitting a physical channel signal using a plurality of subcarriers. That is, the IEEE 802.16 communication system is an OFDM/OFDMA BWA communication system. The IEEE 802.16d communication system provides wireless broadband Internet services to subscriber stations (SSs). The SSs are mobile and are referred to as “mobile subscriber stations (MSSs).”
A configuration of the IEEE 802.16d communication system will now be described with reference to FIG. 1, which illustrates a schematic configuration of a conventional IEEE 802.16d communication system.
Referring to FIG. 1, the IEEE 802.16d communication system has a multi-cell configuration, i.e., has a first cell 100 and a second cell 150, and includes a first base station (BS) 110 managing the first cell 100, a second BS 140 managing the second cell 150, and a plurality of MSSs 111, 113, 130, 151 and 153. Signal transmission/reception between the BSs 110 and 140 and the MSSs 111, 113, 130, 151 and 153 are achieved using the OFDM/OFDMA technologies. The MSS 130 exists in a border area between the first cell 100 and the second cell 150, i.e., a handoff area. That is, if the MSS 130 moves to the second BS 140 while transmitting/receiving signals to/from the first BS 110, its serving BS is changed from the first BS 110 to the second BS 140.
With reference to FIG. 1, the configuration of the conventional IEEE 802.16d communication system has been described. A frame format of a medium access control (MAC) layer in an IEEE 802.16d communication system will now be described with reference to FIG. 2 which illustrates a format of a frame of a conventional IEEE 802.16d communication system.
Referring to FIG. 2, a horizontal axis 245 denotes an OFDMA symbol number, and a vertical axis 247 denotes a subchannel number. As shown in FIG. 2, one OFDMA frame includes a plurality of, e.g., 13, OFDMA symbols. Also, one OFDMA symbol includes a plurality of, e.g., L+1, subchannels. A main purpose of the IEEE 802.16d communication system is to obtain a frequency diversity gain by distributing entire subcarriers used in the IEEE 802.16d communication system, particularly, data subcarriers, to entire frequency bands. Also, the IEEE 802.16d communication system performs a ranging operation in order to adjust a time offset and a frequency offset in a transmission/reception duration and adjust a transmit power. A change from a downlink to an uplink in the IEEE 802.16d communication system is performed for a transmit/receive transition gap (TTG) 251. Also, a change from the uplink to the downlink is performed for a receive/transmit transition gap (RTG) 255. A sync for a transmission/reception duration can be achieved by allocating separate preamble fields 211, 231, 233 and 235 next to the TTG 251 and the RTG 255.
In the frame format of the IEEE 802.16d communication system, a downlink frame 249 includes the preamble field 211, a frame control header (FCH) field 213, a downlink MAP (DL-MAP) field 215, uplink MAP (UL-MAP) fields 217 and 219, a plurality of downlink burst (DL burst) fields, i.e., a DL burst #1 field 223, a DL burst #2 field 225, a DL burst #3 field 221, a DL burst #4 field 227, and a DL burst #5 field 229.
The preamble field 211 is used to transmit a sync signal, i.e., a preamble sequence, for sync acquisition in a transmission/reception duration. The FCH field 213 includes two subchannels and is used to provide basic information on subchannels, ranging, and a modulation method. The DL-MAP field 215 is used to transmit a DL-MAP message, and the UL-MAP fields 217 and 219 are used to transmit an UL-MAP message. Information elements (IEs) included in the DL-MAP message are illustrated in Table 1.
TABLE 1SyntexSizeNotesDL-MAP_IE( ) {DIUC 4 bitsif(DIUC==15) {Extended DIUCvariabledependent IE} else {if(INC_CID==1) {The DL-MAP starts withINC_CID = 0. INC_CIDis toggled between0 and 1 bythe CID_SWITCH_IE ( )N_CID 8 bitsNumber of CIDsassigned for this IEfor(n=0;n<N_CID;n++) {CID16 bits}}OFDMA Symbol Offset10 bitsSubchannel Offset 5 bitsBoosting 3 bits000: normal (not boosted)001: +6 dB010: −6 dB011: +9 dB100: +3 dB101: −3 dB110: −9 dB111: −12 dBNo. OFDMA Symbols 9 bitsNo. Subchannels 5 bits}}
Referring to Table 1, “DIUC” (Downlink Interval Usage Code) denotes a modulation method and a transmission purpose of a current transmission message, and “CID” denotes a CID of each SS corresponding to the DIUC.
“OFDMA Symbol Offset” denotes an offset of symbol resources allocated to the DL bursts, “Subchannel Offset” denotes an offset of subchannel resources allocated to the DL bursts, “Boosting” denotes a power value increased during transmission, “No. OFDMA Symbols” denotes the number of allocated OFDMA symbols, and “No. Subchannels” denotes the number of allocated subchannels.
As shown in Table 1, downlink information of the IEEE 802.16d communication system is represented by combining information on each SS corresponding to the DIUC. Accordingly, each SS analyzes its own data when the DL-MAP message is perfectly demodulated.
IEs included in the UL-MAP message are illustrated in Table 2.
TABLE 2SyntexSizeNotesUL-MAP_IE( ) {CID16 bitsUIUC 4 bitsif(UIUC==12) {OFDMA Symbol10 bitsOffsetSubchannel Offset6  bitsNo. OFDMA Symbols8  bitsNo. Subchannels5  bitsRanging Method 3 bits000: Initial Ranging over two symbols001: Initial Ranging over four symbols010: BW Request/Periodic Ranging over one sysbol011: BW Request/Periodic Ranging over threesymbols100-111: reserved} else if(UIUC==14) {CDMA_Allocation_IE ( )52 bits} else if(DIUC==15) {Extended DIUC dependentvariableIE} else {OFDMA Symbol Offset10 bitsSubchannel Offset 5 bitsNo. OFDMA Symbols 9 bitsNo. Subchannels 5 bitsMini-subchannel index 3 bits000: no mini-subchannels used001: starting with mini-subchannel 1010: starting with mini-subchannel 2011: starting with mini-subchannel 3100: starting with mini-subchannel 4101: starting with mini-subchannel 5110. 111: reserved}}
Referring to Table 2, “CID” denotes a CID of a relevant SS, and “UIUC” (Uplink Interval Usage Code) denotes a modulation method and a transmission purpose of a message that the SS transmits. Since the other values are similar to the values described with reference to Table 1, their detailed description is omitted.
Also, in the frame format of the IEEE 802.16d communication system, an uplink frame 253 includes a ranging subchannel field 243, a plurality of preamble fields 231, 233 and 235, and a plurality of uplink bursts (UL bursts), i.e., a UL burst #1 field 237, a UL burst #2 field 239, and a UL burst #3 field 241.
The ranging subchannel field 243 is used to transmit ranging subchannels for ranging, the preamble fields 231, 233 and 235 are used to transmit a sync signal, i.e., a preamble sequence, for sync acquisition in a transmission/reception duration. Information including CIDs allocated to connections is transmitted using the DL-MAP field 215.
A format of a MAC protocol data unit (PDU) will now be described with reference to FIG. 3, which illustrates a schematic format of a MAC PDU of a conventional IEEE 802.16d communication system.
Referring to FIG. 3, the MAC PDU includes a Generic MAC PDU Header field, a Payload field, and a cyclic redundancy check (CRC) field. The Generic MAC PDU Header field is used to transmit header information for a MAC PDU transmission, the Payload field is used to transmit user data, and the CRC field is used to transmit CRC bits for detecting an error of the MAC PDU.
The Generic MAC PDU Header field includes a header type (“HT”) field, an encryption (“EC”) field, a “Type” field, a reserved (“RSV”) field, a CRC indicator (“CI”) field, an encryption key sequence (“EKS”) field, a length (“LEN”) field, a “CID” field, and a header check sum (“HCS”) field. The “HT” field indicates whether a generic MAC PDU or a bandwidth request message is transmitted. The “EC” field indicates whether a current transmission frame is encrypted. The “Type” field indicates a sub-header type. For example, the “Type” field is represented with 6 bits denoting types shown in Table 3.
TABLE 3TYPESUB HEADER#0ARQ_ACK ALLOCATION SUB HEADERGM SUB HEADER#1PACKING SUB HEADER#2FRAGMENTATION SUB HEADER#3EXTENDED TYPE#4ARQ FEEDBACK PAYLOAD#5MESH SUB HEADER
Referring to Table 3, the “Type” field is represented with 6 bits, and the sub-header type is determined according to a bit value of the “Type” field. That is, bit #0 of the Type field indicates whether an ARQ_ACK allocation sub-header indicating field allocation for transmitting an automatic retransmission request (ARQ) ACK is used or whether a grant management (GM) sub-header for allocating a resource request is used.
Bit #1 of the Type field of the Type field indicates whether a packing sub-header for concatenating and transmitting more than two packets is used when the size of a sub-header packet to be transmitted is smaller than a predetermined size of the sub-header packet.
Bit #2 of the Type field indicates whether a fragmentation sub-header for fragmenting a sub-header packet into more than two packets is used when the size of the sub-header packet is larger than the predetermined size of the sub-header packet.
Bit #3 of the Type field indicates whether an extended type is used.
Bit #4 of the Type field indicates whether an ARQ feedback payload for fast ARQ is used.
Bit #5 of the Type field indicates whether a mesh sub-header for transmitting a packet applied to a mesh network is used.
The “RSV” field is reserved for a future use. The “CI” field indicates whether the MAC PDU uses a CRC. The “EKS” field indicates what kind of encryption key is used, i.e., indicates a kind of an encryption key used in the MAC PDU. The “LEN” field indicates a length of the Payload field of the MAC PDU. The “CID” field indicates a CID of a connection through which the MAC PDU is transmitted. The “HCS” field is used to transmit a HCS used to detect an error of the Generic MAC PDU Header field.
It is assumed that a CID transmitted using the CID field has a 16-bit length, and the CID will now be described.
In order for an MSS to receive services from a BS in a BWA communication system, a connection between the MSS and the BS is established. The connection is established between MAC peers in order to transmit/receive information, i.e., control data and user data, between the MSS and the BS. The number of connections and kinds of the connections are many, and accordingly, CIDs for identifying connections established between the MSS and the BS are allocated. Also, besides the MSS, CIDs can be allocated to all CID-allocatable media. The CID indicates an identification (ID) allocated to each connection by the BS and is transmitted using the Generic MAC PDU Header field. Also, the CID is used for signaling of the MAC layer such as resource allocation and protocol control between the MSS and the BS.
As described above, the CID is a resource necessarily used in signal transmission/reception between the BS and the MSS. However, the CID has a fixed length of 16 bits used in the IEEE 802.16d communication system. As a result, the CID transmission/reception creates overhead in the IEEE 802.16d communication system, decreasing in efficiency of resources.